Triumphrat

koifarm · 03-24-2008

I have been busy surfing to find out the answer to the question we have had posted here before and have the answer.
The question is "How much gas of a particular grade is left in the hose/pump when I gas my bike up?" Or, does the gas get diluted or mixed from the previous gasser at the pump.
This might help:

When we need gasoline for our vehicle and pull up to our local service station, we make a decision on what grade of gasoline we use. This decision is generally based on what the owner's manual recommends. Most service stations in the U.S. carry three grades of gasoline -- regular (87 octane), mid-grade (89 octane), and premium (92 or 93 octane).

The octane rating posted at the pump is actually the average of the motor octane number (MON) and research octane number (RON). The MON determines the octane value of the gasoline with the engine under load conditions while the RON determines the octane no-load condition.

Although using the octane grade specified in the owner's manual is the best practice, there are times when some engines (even new ones) will "ping" using regular gasoline, and a higher octane fuel may be necessary. This happened to me back in the early '80s when I had a vehicle that was supposed to operate on 87 octane, but wouldn't drive safely. I switched to 89 octane, and it ran fine. A higher octane fuel may also be justified when operating a larger vehicle or pulling a heavy boat or trailer which puts a heavier load on the engine.

Some people feel that using a higher octane will improve vehicle performance. This is not necessarily true and is usually a waste of money. However, there are a number of cases reported where a vehicle may have operated on 87 octane for a number of years and over a period of time develops combustion deposits that affect combustion and the octane required for the vehicle. This usually results in poor performance and in many cases can be alleviated by switching to a higher octane gasoline. This is called octane requirement increase (ORI).

But back to our concern about the residual regular grade in the filling hose before one fills up with premium gasoline. Assuming a 10-foot filling hose with an internal diameter of 3/4 inch, the amount of regular gasoline would be 0.229 gallons (V = pr2h, or 3.14 x (0.375 in.)2 x 120 in. x 0.00433 gal/in.3). Assuming a 20-gallon tank and a fill up with a premium of 93 octane (with the hose filled with 87 octane at the start of the fillup), the effect is best described by the equations below:

Octane number =
(0.229 gal/20 gal) (87) +
(19.771 gal/20 gal) (93)
87 octane contribution 93 octane contribution

Octane number = 0.996 + 91.943

Octane number = 92.9

Considering the precision of the octane test procedure is 0.2 octane numbers and the dilution with 87 octane reduces the octane in the tank from 93 to 92.9, We would be better off worrying about getting to church on time than the effect of octane in our bike.

This month's Mr. Whizard is Harry Dietzmann, director of the Petroleum Products Research Department in the Fuels and Lubricants Research Division (08). An SwRI employee for more than 33 years, Dietzmann is a chemist by training whose activities include national fuel surveys, and gasoline and diesel lubricant, gear, automatic transmission fluid, and other automotive fluid qualification testing.

Now, If some of you math wizards out there can figure this one out (i am terrible with math) we will know what the actual octane would be.
It appears though, that the dilution is so minimal, even at the 4 gallon level, it would likely be that you should fill up with high test and thus guarantee the best octane gas for your purposes.
Roughly speaking though, we are probably looking at something like a 92 or better grade if the previous person had used 87 octane and you fill up with high test.
This will be an interesting thread....
Bill

Bluechip · 03-24-2008

I look at from the half full side of the equation. I use 87 and think I might be getting a little of the leftover 93 in my tank.

Really, I don't think it makes much of a differance.

uzidzit · 03-24-2008

Draining 8-12 hoses at 2 am is enough to get home

Loxpump · 03-24-2008

I don't like the fact that I'm leaving gas in the hose that I paid for! I don't know if it matters but I usually try to turn off the pump first then stop the handle, but not all pumps do that. Some when you turn them off the handle no longer opens the nozzle.

Geoff · 03-24-2008

uhh..I guess you mean college.
get any fumes?

g

BillT100 · 03-24-2008

Quote:

Originally Posted by uzidzit

Draining 8-12 hoses at 2 am is enough to get home

Yep, I've done that. Had to push my 69 BSA Lightning about 2 blocks to a closed station at 1 or 2am where I drained 1 hose before the cops pulled up and told me to quit. I think they were somewhat sympathetic to my problem and left first allowing me to drain 2 more hoses which got me home about a mile away.

Gob-ny-geay · 03-24-2008

Shouldn't this post go with the other post on Octane currently active?

1.) Are the hoses really ten feet long. I think more like about 6 or seven, which would lower the amount of gasoline in the hose number by 30-40%?
2.) Why assume the 87 Octane is in the hose? What are the odds of say 93 Octane?
3.) Is it best to "lurk" around the pumps, whistling and acting nonchalant, until you find a pump being used with YOUR preferred octane? Then rush to get in line?
4.) If a person continually nitpicks about minor, insignificant things like this, will life quickly pass him by?
5.) What are "Nits" anyway?

Regards as always,

uzidzit · 03-24-2008

I was going to spell it cottage but I thought that was a little over the top, as a side note for some reason I always left a buck or two under the door of the station, with a note. I have no idea why it just seemed wrong to drain the lines without paying for the gas, anyway maybe it made their day in the morning when they came in.

uzidzit · 03-24-2008

nits are head lice, nit picking got its name from being something you do and do and do, and never really get completely done. hep me before I lose the point of the thread again, fun for the feeble minded.

tomville · 03-24-2008

Quote:

Originally Posted by Loxpump

I don't like the fact that I'm leaving gas in the hose that I paid for! I don't know if it matters but I usually try to turn off the pump first then stop the handle, but not all pumps do that. Some when you turn them off the handle no longer opens the nozzle.

Any fuel you leave in the hose is negated by the fuel that was left by the person before you.